RFR: 8280686: Remove Compile::print_method_impl

[Xin Liu]

This is a follow-up task of JDK-8280274. I think it is still reasonable to only evaluate
"CompilerPhaseTypeHelper::to_string(cpt)" when NOT_PRODUCT is defined, but we can do
that in the function body. We should avoid from messing around interfaces with macros.

Actually, it's not necessary to have print_method_impl as a public interface at all.
The only client of it is print_method().

Here is the current interface of Compile::print_method
V1: print_method(CompilerPhaseType cpt, int level)
V2: print_method(CompilerPhaseType cpt, Node* n, int level)

The only client of V2 is vector.cpp. It attempts to dump the phase name and vec_box node. It's impossible to to have n=NULL. No one will consume property <"phase :NULL">.

I think we should go in this way.

void Compile::print_method(CompilerPhaseType cpt, int level) {
  print_method(cpt, NULL, level);
  }


Testing: 
Verify that igv is still working with PrintIdealGraphLevel=3/4

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Commit messages:
 - Remove Compile::print_method_impl

Changes: https://git.openjdk.java.net/jdk/pull/7229/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7229&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8280686
  Stats: 18 lines in 2 files changed: 4 ins; 11 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7229.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7229/head:pull/7229

PR: https://git.openjdk.java.net/jdk/pull/7229